I'm 40 years old, 5'8", 148 lbs, been biking on and off for 15 years at various levels of commitment, never all that serious.

I just got the results of my blood lactate test and I was surprised to see how low my Lactate Threshold is.
For the first ten months of 2006 my riding consisted of doing 5 or 6 spin classes a week at the gym and riding the entire time high in the anaerobic zone (or riding laps in Central Park at a similar pace), >160 bpm.

About two months ago I decided to try and formulate a real road bike training plan, got Friel's Training Bible and realized I was doing absolutely no riding below threshold. So for the last two months that's what I've been doing most of the time (about 10-12 hours week, 6 of which are outdoors on the the bike, the rest indoors).

My max heart rate is 189, but the results of the test (yes, they took blood) yielded my LT at 156. My power output at threshold was respectable, but I thought the actual heart rate at threshold would be higher than 156. Could this low number be due to ten months of almost exclusively training way above threshold?